Some communication systems support a mode in which voice calls are transported over data packets. The Universal Mobile Telecommunications System (UMTS) standards specified by the Third Generation Partnership Project (3GPP), for example, define a “Circuit-Switched (CS) voice over HSPA” mode in which voice calls are mapped onto High Speed Packet Access (HSPA).
Communication in this mode typically involves both the Radio Link Control (RLC) layer and the Packet Data Convergence Protocol (PDCP) layer of the communication connection. The RLC layer is defined, for example, in “Universal Mobile Telecommunications System (UMTS); Radio Link Control (RLC) Protocol Specification,” 3GPP TS 25.322, version 8.9.0, release 8, June, 2010, which is incorporated herein by reference. The PDCP layer is defined, for example, in “Universal Mobile Telecommunications System (UMTS); Packet Data Convergence Protocol (PDCP) Specification,” 3GPP TS 25.323, version 8.5.0, release 8, February, 2010, which is incorporated herein by reference.
The data transported in UMTS data packets may be encrypted in order to provide data security. Ciphering in UMTS is defined, for example, in “Universal Mobile Telecommunications System (UMTS); LTE; 3G security; Security Architecture,” 3GPP TS 33.102, version 8.6.0, release 8, April, 2010, which is incorporated herein by reference.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.